Vol 458 | 26 March 2009 | doi:10.1038/nature07920 LETTERS

The impact and recovery of 2008 TC3 P. Jenniskens1, M. H. Shaddad2, D. Numan2, S. Elsir3, A. M. Kudoda2, M. E. Zolensky4,L.Le4,5, G. A. Robinson4,5, J. M. Friedrich6,7, D. Rumble8, A. Steele8, S. R. Chesley9, A. Fitzsimmons10, S. Duddy10, H. H. Hsieh10, G. Ramsay11, P. G. Brown12, W. N. Edwards12, E. Tagliaferri13, M. B. Boslough14, R. E. Spalding14, R. Dantowitz15, M. Kozubal15, P. Pravec16, J. Borovicka16, Z. Charvat17, J. Vaubaillon18, J. Kuiper19, J. Albers1, J. L. Bishop1, R. L. Mancinelli1, S. A. Sandford20, S. N. Milam20, M. Nuevo20 & S. P. Worden20

In the absence of a firm link between individual and magnitude H 5 30.9 6 0.1 (using a phase angle slope parameter their asteroidal parent bodies, are typically characterized G 5 0.15). This is a measure of the asteroid’s size. only by their light reflection properties, and grouped accordingly Eyewitnesses in and at Station 6 (a train station between into classes1–3. On 6 October 2008, a small asteroid was discovered Wadi Halfa and Al Khurtum, ) in the Nubian Desert described a with a flat reflectance spectrum in the 554–995 nm wavelength rocket-like fireball with an abrupt ending. Sensors aboard US govern- range, and designated 2008 TC3 (refs 4–6). It subsequently hit the ment satellites first detected the at 65 km altitude at Earth. Because it exploded at 37 km altitude, no macroscopic 02:45:40 UTC (ref. 8). The optical signal consisted of three peaks span- fragments were expected to survive. Here we report that a dedicated ning 3.5 s, with most of the radiated energy in the middle 1-s pulse at search along the approach trajectory recovered 47 meteorites, an inferred altitude of about 37 km, and a final pulse 1 s later. Meteosat fragments of a single body named Almahata Sitta, with a total 8 (ref. 9) detected the brightest optical signal when the asteroid was at of 3.95 kg. Analysis of one of these meteorites shows it to be an 37.5 6 1.0 km. Rapidly fading infrared radiation was detectable down , a polymict , anomalous in its class: ultra-fine- until at least 32.7 6 0.7 km. The 10-mm Si–O band of glowing dust was grained and porous, with large carbonaceous grains. The combined the dominant feature in a seven-channel 6–13 mm infrared spectrum asteroid and reflectance spectra identify the asteroid as taken ,1 s after the explosion. The height of the dust cloud was F class3, now firmly linked to dark carbon-rich anomalous , 35.7 6 0.7 km. Independently, we measured this altitude at 35– a material so fragile it was not previously represented in meteorite 42 km, with no significant dust deposition below 33 km, based on collections. UK Meteorological Office10 wind model data and ground-based The asteroid was discovered by the automated images of the lingering train11 taken from Wadi Halfa at sunrise telescope at Mount Lemmon, Arizona on October 6 06:39 UTC (ref. 4). (03:22–03:27 UTC). Early orbital solutions showed an impact 19 h after discovery with a Unexpectedly, some meteorites survived the explosion. Fifteen predicted impact location in the Nubian Desert of northern Sudan5,6 fresh-looking meteorites with a total mass of 563 g were recovered (Table 1). Numerous astronomical observatories imaged the object by 45 students and staff of the University of during a field until it entered the Earth’s umbra on October 7 01:49 UTC.Inthe campaign on 5–8 December 2008. A second search on 25–30 previous two , its brightness oscillated with an amplitude of December (72 participants) raised the total to 47 meteorites and 1.02 mag at main periods of 49.0338 6 0.0007 s and 96.987 6 0.003 s, 3.95 kg. range from 1.5 g to 283 g, spread for 29 km along and their harmonics, revealing that the asteroid was in a non-principal- the approach path in a manner expected for debris from 2008 TC3 axis rotation state7. The oscillation was centred on absolute visible (Fig. 1). Nearly all recovered meteorites show a broken face with no corres- Table 1 | Orbital parameters of 2008 TC used to calculate the approach 3 ponding pieces nearby (Fig. 2). One intact fully crusted meteorite was path perfectly oriented in flight, with only a single side exposed to the Symbol Parameter Value oncoming air stream and one rotational of freedom (Fig. 2e), a Semimajor axis 1.308201 6 0.000009 AU suggesting that this secondary fragmentation was caused by centri- q Perihelion distance 0.899957 0.000002 AU 6 fugal forces or uneven dynamic pressure from rapid tumbling. v Argument of perihelion 234.44897 6 0.00008u V Longitude of ascending node 194.101138 6 0.000002u Almahata Sitta is a fine-grained fragmental breccia. A small 1.5 g i Inclination 2.54220 6 0.00004u meteorite (no. 7) was broken under 35 lb peak pressure to create a 2008 20 3989 0 0001 Tp Perihelion time November . 6 . UT fresh surface for analysis—all results reported here are from this These parameters are JPL solution 15; equinox J2000, 2008 October 07.0 TDB or Barycentric meteorite. It had a tensile strength of only 56 6 26 MPa, cracking Dynamical Time. The astrometric position of 295 observations were used. This ephemeris, when projected to an altitude of 50 km, predicts an entry velocity of 12.42 km s21 at a shallow along a white layer, rich in pyroxene, sprinkled with darker areas rich 20u angle relative to the surface, with a perpendicular uncertainty in position of only 6100 m. in carbonaceous matter (Fig. 2a).

1SETI Institute, Carl Sagan Center, 515 North Whisman Road, Mountain View, 94043, USA. 2Physics Department, University of Khartoum, PO Box 321, Khartoum 11115, Sudan. 3Physics Department, Juba University, Juba, Sudan. 4NASA , Mail Code KT, , Texas 77058, USA. 5Jacobs Technologies Engineering Science Contact Group (ESCG), Johnson Space Center, Houston, Texas 77058, USA. 6Department of Chemistry, Fordham University, 441 East Fordham Road, Bronx, New York 10458, USA. 7Department of Earth and Planetary Sciences, American Museum of Natural History, 79th Street at Central Park West, New York, New York 10024, USA. 8Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC 20015-1305, USA. 9Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. 10School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK. 11Armagh Observatory, College Hill, Armagh BT61 9DG, UK. 12Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada. 13ET Space Systems, 5990 Worth Way, Camarillo, California 93012, USA. 14Sandia National Laboratories, PO Box 5800, Albuquerque, New Mexico 87185, USA. 15Clay Center Observatory, Dexter and Southfield Schools, 20 Newton Street, Brookline, Massachusetts 02445, USA. 16Astronomical Institute of the Academy of Sciences, Fricˇova 298, 25165 Ondrˇejov Observatory, Czech Republic. 17Czech Hydrometeorological Institute, Na Sabatce 17, 143 06 Praha 4, Czech Republic. 18Institut de Me´canique Ce´leste et de Calcul des E´phe´me´rides, 77 avenue Denfert-Rochereau, 75014 Paris, France. 19Dutch Meteor Society, Akker 141, 3732 XD De Bilt, The Netherlands. 20NASA Ames Research Center, Mail Stop 245-6, Moffett Field, California 94035, USA. 485 ©2009 Macmillan Publishers Limited. All rights reserved LETTERS NATURE | Vol 458 | 26 March 2009

Figure 1 | Map of the Nubian Desert of northern Sudan with the ground- fragments would have stopped ablating at around 32 km altitude, falling projected approach path of the asteroid and the location of the recovered vertically on the ground at 30–60 m s21. Labels in white rectangles mark the meteorites. 2008 TC3 moved from a geodetic longitude of 31.80381u E and position where meteorites of indicated masses are predicted to have fallen latitude of 120.85787u N at 50 km altitude, to 32.58481u E, 120.70569u Nat (calculations assume spheres released at 12.4 km s21 from detonation at 20 km altitude above the WGS-84 ellipsoid. White arrow represents the path 37 km altitude, white star). In light yellow is shown the area that was of the 2008 TC3 fireball with the projected, non-decelerating ground path systematically searched. Special attention was given to possible large represented as a thin black line (altitude labels in km, within white ovals). fragments further down track, but none were found. Such larger masses The sizes of the red symbols indicate small (1–10 g), medium (10–100 g) and would have carried residual forward velocity. The yellow line marks the path large (100–1,000 g) meteorites. Our dark-flight calculations show that 270-g of the local train tracks with the location of Station 6 labelled.

Classification of the meteorite was based on oxygen isotopes, bulk of the material being a residue of partial melting13,14. The relatively chemistry, and mineralogy. The oxygen isotope abundance of two high ($0.1 CI) REE abundances in Almahata Sitta are consistent with fragments was measured as: D17O 520.147% and 20.501%, it being a polymict ureilite, which as a group have higher REE con- d17O 5 3.90% and 3.56%, and d18O 5 7.70% and 7.72% relative centrations than the more common monomict ureilites14. (The ‘poly- to Standard Mean Ocean Water (SMOW). A third sample, in contact mict’ modifier refers to the presence of olivine and pyroxene-rich with fusion crust, gave D17O 520.539%, d17O 5 3.09%,and lithic clasts among ureilitic clasts.) The sample has subrounded d18O 5 6.89% SMOW. These values scatter along the carbonaceous mineral fragments and fine-grained olivine aggregates embedded in chondrite anhydrous mineral (CCAM) slope of d17O/d18O, on the a cataclastic matrix of ureilitic material (Fig. 3A, B)15. Only one case of upper edge of the compositional field of ureilites12—see zoned olivine was found. Shock effects are not apparent. The Supplementary Information. Bulk chemistry shows that trace element examined samples have considerable porosity, ranging from 10% to abundances are achondritic (tabulated in Supplementary 25%; the walls of pores are commonly coated by anhedral to euhedral Information). Rare earth element (REE) abundances relative to CI crystals of low-calcium pyroxene (Fs2Wo3) and olivine (Fa12-14), and chondrites steadily increase with atomic number from 0.1 to 0.6 CI, in some instances spherules of kamacite and botryoidal masses of Cr- and possess a distinct negative Eu anomaly, closely resembling the bearing troilite (Fig. 3C). (Here Fs indicates ferrosilite, Wo wollasto- bulk analyses of many ureilites, and generally interpreted as indicative nite, Fa fayalite, and Fa12-14 indicates 12–14% of this component.) These could be vapour deposits. Aggregates of carbonaceous material, ab c up to 0.5 mm in size, are common and primarily consist of fine- grained graphite, making the rock dark. Some diamond and aliphatic carbon is also present (Fig. 3D). On the basis of the above information, Almahata Sitta is classified as an anomalous polymict ureilite14,16. Ureilites are coarse-grained, ultramafic rocks believed to be either magmatic cumulates or partial melt residues. Mineral compositions of Almahata Sitta are not anom- alous, but the textures are, including rare zoning of olivine, larger size carbonaceous aggregates, fine-grained texture, high metal content, and high porosity with possible vapour-phase mineral growth of d e f olivine (consistent with rapid cooling of an impact-produced melt). Other ureilites have a bulk density of 3.05 6 0.22 g cm23 and an average micro-porosity of 9% (range 6–20%)17. The bulk density of Almahata Sitta varies from fragment to fragment. The most precisely measured values (in g cm23) are 2.10 6 0.06 (no. 14, 152.6 g) and Figure 2 | Macroscopic features of the Almahata Sitta meteorite. 2.50 6 0.08 (no. 16, 171.1 g). Assuming an average ureilite grain a, Evidence of clasts in meteorite no. 7 (1 cm diameter) in a fresh fracture density17 of 3.35 g cm23, this puts the porosity of Almahata Sitta in surface induced by pressure in the laboratory. b, Meteorite no. 15 (4 cm the 25–37% range, equal to the high porosities of primitive carbona- diameter), in situ, shows rounded shape of ablated surface. c, Meteorite no. 4 ceous chondrite meteorites17. (14 g), placed on aluminium foil, shows the dark interior of a surface The recovered meteorites represent only ,0.005% of the initial fractured upon impact. d, Meteorite no. 14 (2 3 7 cm), in situ, shows millimetre-sized grains in a weathered surface that was broken before mass, derived as follows: most are darker than the fractured surface impact. e, Back side of perfectly oriented meteorite no. 5 (10.9 g), with a front of no. 7 (Fig. 2). Using the V-band albedo of 0.046 6 0.005, measured shell exhibiting thick radially flowing crust and a thinly crusted aft-shell. for the dark phase of the meteorite, the asteroid’s absolute visual mag- f, The very homogeneous course-grained broken surface of large meteorite nitude translates to an asteroid diameter of 4.1 6 0.3 m (ref. 18). If the no. 16 (10 cm diameter). density were 2.3 6 0.2 g cm23, then the pre-atmospheric mass was 486 ©2009 Macmillan Publishers Limited. All rights reserved NATURE | Vol 458 | 26 March 2009 LETTERS

a 0.11 A B

0.10

0.09

0.08 C D Reflectance

0.07

0.06 600 700 800 900 1,000 b 0.15

Figure 3 | Petrography15 of Almahata Sitta. A, Large-scale back-scattered electron view showing high- and low-porosity lithologies; arrows indicate large carbonaceous inclusions; most olivine and pyroxene aggregates have 0.10 interstitial silicates whose Si-content increases adjacent to metal grains. Mineral fragments include polycrystalline olivine (Fa8-15; CaO 5 0.15–0.51 wt%; Cr2O3 5 0.03–1.58 wt%), low-calcium pyroxene (Fs2Wo5–Fs17Wo4;Cr2O3 5 0.33–1.02 wt%), pigeonite (Fs15Wo5–Fs18Wo11;Cr2O3 5 0.72–1.11 wt%) and carbonaceous Reflectance aggregates, kamacite (Fe0.92Ni0.08–Fe0.96Ni0.04) and troilite. Some clasts 0.05 consist of rounded pyroxene grains containing an abundant Fe-rich nanophase. B, Low-porosity grains show rounded crystals. Some carbonaceous areas (c) and a few pores (p) are marked. C, Pore containing euhedral to anhedral olivine and pyroxene crystals. D, A large carbonaceous aggregate containing dispersed, fine-grained troilite and kamacite, the latter 0.00 containing Si and P. Note the high porosity (p). Raman spectra measure the 500 1,000 1,500 2,000 2,500 carbonaceous grains to be amongst the most graphitic of any meteorite yet Wavelength (nm) studied, with a G band centre and full-width at half-maximum of 1,572 6 2.1 21 and 42 6 5cm , respectively. Imaging Raman shows grain sizes of ,30 mm Figure 4 | Meteorite reflectance spectrum compared to that of asteroid m with slightly higher aromatic order near the rim. Two 10- m-sized nano- 2008 TC3.a, The meteorite spectrum (circles and thick black line) is diamonds were imaged in their host material, showing D band peak shifts measured at 3–7 nm resolution relative to a diffuse reflectance standard. The from latent or biaxial strain. Aliphatic carbon is present too, with weak asteroid spectrum (shown as vertical lines, representing the s.d. of each set of 21 aliphatic CH-stretch vibration bands peaking at 2,968, 2,921 and 2,852 cm 10 measured points) is measured at 4 nm resolution relative to the solar (ref. 23). analogue star 16 Cyg B. We used the 4.2 m William Herschel Telescope and ISIS spectrograph on 6 October at 22:22–22:28 UTC. The Sun–asteroid–Earth phase angle was 18.6 . The asteroid spectrum was scaled vertically to match 6 6 3 12 u 83 25 t and the kinetic energy of impact (6.4 1.9) 10 J(at the albedo of the broken surface of meteorite no. 7 (Fig. 2a). Techniques used 50 km). This compares well with our estimate calculated from acoustic to measure the meteorite spectrum: l , 700 nm, freshly broken surface no. 7, signals from the fireball detected at the Kenyan infrasonic array I32KE: using a fibre-fed Ocean Optics spectrometer at an illumination angle of 20u 12 (6.7 6 2.1) 3 10 J. Analysis of the bolide light curve shows that the and near-perpendicular viewing (circles); l 5 350–2,500 nm, scraped total radiated energy was about 4.0 3 1011 J (ref. 7), which translates meteorite surface (thick black line), using a FieldSpec ProFR spectrometer empirically19 to a pre-atmospheric kinetic energy of ,4 3 1012 J, in from Analytical Spectral Devices, with reflectance values scaled vertically to good agreement. match visible albedo data. b, Same data (2008 TC3 shown as grey vertical It is unsurprising that such meteorites have not been collected lines: meteorite no. 7 shown as grey circles and as thick black line over 350–2,500 nm wavelength range) compared to the average reflectance before. The asteroid started to break apart at an altitude of 46– spectra of low albedo asteroid taxonomic classes G, B, C, F, T, P and D24–27. 42 km, when the ram pressure was only 0.2–0.3 MPa, and terminated Note that individual asteroids within a class show a range of albedo. Long- in catastrophic disruption at a pressure of only 1 MPa. The fireball PE- wavelength near-infrared reflectance was independently measured using a criterion20, which uses a fireball’s observed end height, velocity, mass Biorad Excalibur Model 3000 Fourier-transform infrared spectrometer and entry angle as a proxy for estimating its physical structure, would (circles). make this a IIIb/a-type, normally associated with cometary debris (which tends to disrupt at pressures of #0.1 MPa). In comparison, telluric water, the meteorite spectra showing none of the substructure 23 the unusual Tagish Lake meteorite was similar in initial mass, entry diagnostic of many phyllosilicates , and implies that 2008 TC3 was angle, peak luminosity and light-curve shape, but penetrated deeper F class. Other low-albedo asteroid types are redder, while B and G into the atmosphere, breaking at 40–29 km, with ablation continuing classes have a steep drop-off below 400 nm, unlike the meteorite until 27 km (PE 5 IIIa/II)21. (Fig. 4b)24–27. The average asteroid F-class spectrum has a slightly Ureilites were initially thought to derive from S-class asteroids22 in more bluish slope (being more reflective in the blue relative to longer the Tholen3 classification of asteroid reflectance spectra. However, wavelengths) below 700 nm, similar to that of a scraped meteorite the reflectance spectra of 2008 TC3 and Almahata Sitta meteorite no. surface (Fig. 4b), and a slightly steeper slope above 1,500 nm. 7 are most similar to B or F class asteroids (Fig. 4a). Unlike B-class F-class asteroids comprise only ,1.3% of asteroids. Backward objects, the meteorite has no hydrated minerals and a modest 3-mm integrations of Monte Carlo clones of the orbit of 2008 TC3 show OH-stretch vibration band. This is indicative of minor adsorbed that there is an evolutionary pathway, driven by interactions with 487 ©2009 Macmillan Publishers Limited. All rights reserved LETTERS NATURE | Vol 458 | 26 March 2009

Earth, originating from orbits similar to only one other known 21. Brown, P. G., ReVelle, D. O., Tagliaferri, E. & Hildebrand, A. R. An entry model for the Tagish Lake fireball using seismic, satellite and records. Meteorit. F-class asteroid: the 2.6-km sized (152679) 1998 KU2. Other candi- Planet. Sci. 37, 661–675 (2002). date parent bodies may be identified in the future. 22. Gaffey, M. J. et al. Mineralogic variations within the S-type asteroid class. Icarus 106, 573–602 (1993). Received 6 February; accepted 20 February 2009. 23. Sandford, S. A. The mid-infrared transmission spectra of Antarctic ureilites. Meteoritics 28, 579–585 (1993). 1. Lauretta, D. S. & McSween, H. Y. Jr (eds) Meteorites and the Early Solar System II 24. Hiroi, T., Zolensky, M. E. & Pieters, C. M. Discovery of the first D-asteroid spectral (Univ. Arizona Press, 2006). counterpart: Tagish Lake meteorite. Lunar Planet. Sci. Conf. 32, abstr. 1776 (2001). 2. Vernazza, P. et al. Compositional differences between meteorites and near-Earth 25. Tholen, D. J. Asteroid Taxonomy from Cluster Analysis of Photometry. Ph.D. Thesis, asteroids. Nature 454, 858–860 (2008). Univ. Arizona (1984). 3. Tholen, D. J. in Asteroids II (eds Matthews, M. S., Binzel, R. P. & Gehrels, T.) 26. Zellner, B., Tholen, D. J. & Tedesco, E. F. The eight-color asteroid survey: Results 1139–1150 (Univ. Arizona Press, 1989). for 589 minor planets. Icarus 61, 335–416 (1985). 4. Kowalski, R. A. et al. in MPEC 2008–T50 (ed. Williams, G. V.) 1–1 ( 27. Bell, J. F. Mineralogical clues to the origins of asteroid dynamical families. Icarus Center, Smithsonian Astrophysical Observatory, 2008). 78, 426–440 (1989). 5. Yeomans, D. NASA/JPL Near-Earth Object Program Office Statement Æhttp:// neo.jpl.nasa.gov/news/news159.htmlæ (6 October 2008). Supplementary Information is linked to the online version of the paper at 6. Chesley, S., Chodas, P. & Yeomans, S. NASA/JPL Near-Earth Object Program www.nature.com/nature. Office Statement Æhttp://neo.jpl.nasa.gov/news/2008tc3.htmlæ (4 November Acknowledgements We thank the University of Khartoum for support of the field 2008). campaigns, and students and staff of the Physics Department of the Faculty of 7. Pravec, P. et al. Tumbling asteroids. Icarus 173, 108–131 (2005). Sciences for their efforts to recover the meteorites. P.J. is supported by the NASA 8. Brown, P. G. US Government release: Bolide detection notification 2008–282 (15 Planetary Astronomy program. D.R. acknowledges the support of NASA’s October 2008); Æhttp://aquarid.physics.uwo.ca/,pbrown/usaf/usg282.txtæ. Cosmochemistry program (grant NNX07AI48G). A. Alunni, J. Travis-Garcia and 9. Borovicka, J. & Charvat, Z. 2008 TC_3. IAU Circ. No. 8994 (2008). L. Hofland of NASA Ames Research Center, and J. Herrin of NASA Johnson Space 10. Swinbank, R. & O’Neill, A. A. A stratosphere-troposphere data assimilation Flight Center, provided laboratory assistance. The work conducted at JPL/Caltech system. Mon. Weath. Rev. 122, 686–702 (1994). was under contract with NASA. The William Hershel Telescope is operated on the 11. Elhassan, M., Shaddad, M. H. & Jenniskens, P. On the trail of 2008 TC3. island of La Palma by the Isaac Newton Group in the Spanish Observatorio del (Astronomy Picture of the Day, NASA Goddard Space Flight Center, 8 November Roque de los Muchachos of the Instituto de Astrofı´sica de Canarias. 2008); Æhttp://apod.nasa.gov/apod/ap081108.htmlæ. 12. Clayton, R. N. & Mayeda, T. K. Oxygen isotope studies of . Geochim. Author Contributions P.J., M.H.S., D.N., S.E. and A.M.K. led the field search for Cosmochim. Acta 60, 2681–2708 (1996). meteorites. M.E.Z., L.L. and G.A.R. performed the petrographic analysis. J.M.F. 13. Goodrich, C. A., Van Orman, J. A. & Wilson, L. Fractional melting and smelting on performed the trace element bulk chemistry analysis. D.R. performed the oxygen the ureilite parent body. Geochim. Cosmochim. Acta 71, 2876–2895 (2007). isotope analysis. A.S. performed the Raman analysis. S.R.C. calculated the orbit and 14. Mittlefehldt, D. W., McCoy, T. J., Goodrich, C. A. & Kracher, A. Non-chondritic ground track. A.F., S.D., H.H.H. and G.R. observed and analysed the astronomical meteorites from asteroidal bodies. Rev. Mineral. 36, 1–195 (1998). spectrum. P.G.B. analysed the infrasound data. P.G.B., W.N.E. and P.J. performed 15. Zolensky, M. et al. Andreyivanovite: A second new phosphide from the Kaidun dark-flight calculations. S.P.W., E.T., M.B.B. and R.E.S. facilitated and analysed the meteorite. Am. Mineral. 93, 1295–1299 (2008). US Government satellite observations. R.D. and M.K. observed the asteroid light 16. Goodrich, C. A. Ureilites: A critical review. Meteoritics 27, 327–353 (1992). curve, which was analysed by P.P., J.B. and Z.C. analysed the Meteosat 8 observations. P.J. and J.V. investigated the link with possible other parent bodies. 17. Britt, D. T. & Consolmagno, S. J. Stony meteorite porosities and densities: A review J.K. provided wind model data. J.A. and P.J. analysed train wind drift. J.L.B. and P.J. of the data through 2001. Meteorit. Planet. Sci. 38, 1161–1180 (2003). measured reflection spectra of the meteorite. R.L.M. and P.J. obtained optical 18. Pravec, P. & Harris, A. W. Binary asteroid population. I. Angular momentum imaging of the meteorite. S.A.S., S.N.M., M.N. and P.J. performed the mid-infrared content. Icarus 190, 250–259 (2007). analysis. 19. Brown, P., Spalding, R. E., ReVelle, D. O., Tagliaferri, E. & Worden, S. P. The flux of small near-Earth objects colliding with the Earth. Nature 420, 294–296 (2002). Author Information Reprints and permissions information is available at 20. Ceplecha, Z. et al. Meteor phenomena and bodies. Space Sci. Rev. 84, 327–471 www.nature.com/reprints. Correspondence and requests for materials should be (1998). addressed to P.J. ([email protected]).

488 ©2009 Macmillan Publishers Limited. All rights reserved